The present invention relates to a semiconductor device and a fabrication method for the same, and more particularly to a semiconductor device having memory cells and diodes for protection and a fabrication method for the same.
Structures having diffusion bit lines and word line electrodes orthogonal to the diffusion bit lines are essential for miniaturization of memory cells. In particular, a structure having bit line insulating films formed on diffusion bit lines by chemical vapor deposition (CVD), not by thermal oxidation, is superior to others in the effect of miniaturizing memory cells. As an example of a method of forming bit line insulating films by CVD, a method is disclosed in which word line electrodes are provided as multilayer electrodes each composed of a lower electrode and an upper electrode both made of polysilicon and the like. In this method, bit line insulating films can be embedded after diffusion bit lines is patterned using a polysilicon film that is to be lower electrodes as a mask (see Japanese Laid-Open Patent Publication No. 2000-332139, for example).
With the progress in miniaturization of memory cells, protection of memory cells from in-process charging has become increasingly important. For this reason, formation of diodes for protection together with memory cells has been examined.
Providing word line electrodes as multilayer electrodes has a merit that diodes for protection can be easily formed. To state more specifically, openings exposing the substrate may be formed using the polysilicon film that is to be lower electrodes as a mask, so that a polysilicon film that is to be upper electrodes can be in direct contact with the substrate via the openings, to thereby form diodes each having a diode electrode directly coupled with the substrate.